In recent years, thanks to the improvement of surgical skills and the application of new comprehensive treatments, more patients with rectal cancer have been able to preserve the anus. However, up to 60-90% of patients may experience varying degrees of bowel function and anal dysfunction after anal preservation surgery. In mild cases, this is manifested by an increased number of bowel movements, and in severe cases, fecal incontinence and emptying disorders. This syndrome caused by various changes in bowel function after anterior rectal resection is called anterior rectal resection syndrome (ARS).ARS seriously affects the quality of life of patients after surgery and often causes incomprehension and misgivings among patients. Here we share with you the clinical manifestations, possible mechanisms and prevention methods of anterior resection syndrome.
I. Definition of ARS
ARS symptoms are complex and diverse, including fecal incontinence, fecal difficulty and constipation. At present, no unified and objective quantitative index has been established at home and abroad to determine the true incidence and severity of ARS, which has caused some difficulties in its accurate definition and classification. Therefore, the current definition of ARS is mainly based on expert consensus and clinical experience. From a practical clinical point of view, ARS can be defined as a variety of intestinal dysfunction with fecal disturbance as the main manifestation after anterior rectal resection due to structural changes in the rectum, tissue damage such as sphincter and nerve, and decreased rectal pouch function and fecal reflex.
II. Classification and clinical manifestations of ARS
ARS can be divided into two types.
(1) urgent incontinence type: mainly manifested by an increase in the number of fecal excretion, which can exceed 10 times/d in severe cases, and a decrease in the ability to control fecal excretion and exhaustion, or even complete incontinence, accompanied by a sense of fecal urgency.
(2) Emptying disorder type: Due to the narrowing of the anastomosis and other reasons, patients have extreme effort to evacuate feces, incomplete emptying, long toilet time and little fecal discharge, and sometimes it takes several days to accumulate feces to form enough pressure to make fecal discharge. According to the literature, the incidence of the urgent incontinence type and the impaired voiding type are 0-71% and 12%-74%, respectively. It is worth noting that these two types overlap with each other.
ARS severely affects patients’ daily life and social functioning, and the quality of life of patients with anal preservation is no better than that of patients who undergo combined rectovaginal perineal resection (APR). A recent Meta-analysis concluded that patients with APR and AR had comparable postoperative quality of life. It is commonly believed that the appearance of ARS is temporary, and that its symptoms are more pronounced 1 year after surgery when anal sphincter function has not yet entered a stable state, but most will gradually resolve after 1 year. However, it has been reported that the discomfort can last up to 15 years in a few patients.
III. Diagnosis and evaluation of ARS
The EORTC QLQ-C30 is the most widely used scale in the world and is based on the overall quality of life, social functioning, general status, disease symptoms and economic status. It requires patients to answer 5 questions about fecal habits and classifies patients with ARS into asymptomatic, mild, and severe disease according to their scores, which is easier to use and its reliability and usefulness have been verified in large international studies.
IV. Pathogenesis of ARS
It is generally accepted that ARS should be influenced by multiple factors and is the combined result of permanent changes in rectal structure as well as short-term postoperative bowel dysfunction. Possible mechanisms include impaired anal sphincter function, reduced rectal volume and compliance, abnormal gastrointestinal dynamics, and reduced neorectal sensitivity due to impaired efferent nerves.
1. Anal sphincter and nerve damage.
It is well known that the anal sphincter includes the internal and external sphincters. The internal sphincter is a non-random smooth muscle, mainly responsible for keeping the anus closed, and is innervated by the pelvic visceral nerve plexus. The external sphincter is under autonomic control and is innervated by the intramural plexus formed by the first branch of the pudendal nerve, the inferior rectal nerve, bilaterally. Injury to the internal sphincter structure or its nerves will result in passive fecal incontinence, i.e., unconscious leakage of rectal contents, whereas injury to the external sphincter will cause fecal urgency and urge fecal incontinence, in which fecal and gas leakage is perceived but not controlled. The innervation of the internal sphincter may be damaged during intraoperative freeing of the rectum, and in addition, intra-anal canal instrumentation is a causal factor for internal sphincter injury. The external sphincter structures are less frequently damaged during anterior resection, and their dysfunction is mainly attributed to injury to the intramural plexus caused during dissection of the pelvis.
2. Damage to rectal structures and volume reduction.
The lower rectal cavity is enlarged and forms the rectal potbelly, which is the site of stool storage and also the receptor of the fecal reflex. The rectal wall is stimulated when there is enough feces in the rectal pot belly, and the peristalsis of the descending colon, sigmoid colon and rectum is enhanced through reflex action, while the internal and external sphincter (effector) of the anal canal is relaxed and the feces is expelled. After removal of the rectum, the sigmoid colon will be anastomosed with the lower rectum or anal canal. The sigmoid colon has a thin diameter and small volume, and its ability to store feces is much less than that of the rectum. The limited volume of the residual rectum, coupled with damage to the receptors and effectors of the fecal reflex, leads to fecal urgency, incontinence, or retention. Some studies have investigated the relationship between anastomotic height or residual rectal length and rectal function after anterior resection, and found that bowel function decreases with the shortening of residual rectal length, and the ability to empty and control feces is better in those with higher anastomotic levels than in patients with lower levels.
3. Anastomotic stricture and sclerotomy tube formation.
In addition to rectal volume, decreased rectal compliance is another important factor in the occurrence of ARS. In the postoperative follow-up, some patients with ARS have hard scarring and stenosis in the anastomosis and adjacent intestinal canal during rectal palpation, losing the original compliance of normal colorectum, which is clinically referred to as “hard canal”, and in severe cases, it appears as “hole-like stenosis” under endoscopy. It has been reported in the literature that there is a direct link between reduced rectal compliance and incontinence symptoms. The formation of sclerotomies may be related to the narrowing of the lumen due to excessive proliferation of collagen fibers and scar contracture during anastomotic healing, especially in the case of anastomotic fistula. The causes of anastomotic stenosis are varied, and it is generally believed that the lower the anastomotic site, the greater the likelihood of anastomotic stenosis. Inadequate freeing of the proximal colon during surgery and high anastomotic tension may cause ischemic contracture of the anastomosis, resulting in stenosis. In addition, with the widespread use of protective ileostomy, the rectum is in an open state for several months after fecal diversion, and the intestinal tube undergoes disuse atrophy, which may cause serious ARS after the stoma is returned.
4. Preoperative radiotherapy.
At present, both domestic and international guidelines recommend preoperative neoadjuvant radiotherapy or radiotherapy for low to intermediate locally progressive rectal cancer (T3-4N0 or TanyN1-2). However, while reducing local recurrence and improving the rate of anal preservation, radiotherapy may cause rectal tissue damage and dysfunction. One study showed that patients who received neoadjuvant radiotherapy and surgery had twice the incidence of persistent bowel dysfunction than patients who received surgery alone, and data from the Dutch TME trial showed that preoperative short-course radiotherapy patients had higher frequency and severity of fecal incontinence at 5 years postoperatively than patients who received surgery alone. A study by some scholars found that severe ARS occurred after receiving radiotherapy even if the length of the residual rectum was greater than 4 cm. how to find a balance between reducing the local recurrence rate and protecting rectal function will be a direction that oncologic surgeons and radiologists will strive to explore in the future.
5. Intestinal coordination dysfunction.
Emptying disorder type of ARS shows reduced number of fecal evacuation, incomplete rectal emptying and extreme effort in fecal evacuation. One possible mechanism of rectal emptying disorder is the loss of rectal coordination function, such as decreased rectal contraction or paradoxical contraction of the anal canal. As a result of prolonged overexertion to evacuate feces, pelvic floor muscle relaxation may occur and its power to assist in contraction of the anal canal is reduced; after nerve injury, a synergistic disorder of the pelvic floor muscle occurs and the external sphincter or puborectalis muscle is unable to relax or paradoxically contracts during fecal evacuation attempts, paradoxically preventing fecal evacuation. This may be related to damage to the nerves innervating the rectum during pelvic dissection. In addition, after the rectum is removed, the recto-colonic reflex will be disturbed and the negative feedback effect on colonic motility will be reduced, resulting in enhanced colonic activity.
V. Prevention and treatment strategies
The treatment of ARS is still unsatisfactory, lacking effective treatment tools, and relying mainly on clinical experience for symptomatic treatment. In addition, some special treatments are beginning to be used in clinical practice.
1.General treatment.
For transient postoperative functional disorders of the intestine, corresponding symptomatic treatment can be given, such as the application of drugs that resist intestinal peristalsis (loperamide) and antispasmodics (scopolamine). Together with dietary regulation, eating more fiber-rich foods, increasing exercise, replenishing necessary water, and adopting correct fecal posture, most symptoms will gradually disappear with time. However, for disorders caused by permanent changes in rectal anatomy, further special prevention and treatment methods are needed.
2. Improved reconstruction techniques and fine intraoperative operations.
The unsatisfactory results of the traditional end-to-end colon-rectum or colon-anal tube anastomosis have prompted scholars to develop new reconstruction modalities, including end-to-side anastomosis, creation of colonic storage pouches and transverse coloplasty. The literature reports that colonic storage pouches can delay or alleviate ARS symptoms, and they can function better for fecal control 1 to 2 years after surgery. The size of the pouch is 5 cm, and the incidence of postoperative constipation and difficult fecal evacuation increases significantly when the pouch is too large. Transverse coloplasty is performed by making a longitudinal incision of 4-5 cm at the end of the proposed anastomosis and suturing it transversely to form a pouch-like structure, which is similar to a J-shaped pouch. However, none of these reconstructive techniques has shown significant long-term benefit beyond 1 to 2 years postoperatively. Surgeons should take special care to protect the nerve intraoperatively, which is extremely important for the preservation of the patient’s fecal and urinary output as well as sexual function. Endorectal manipulations (e.g., using anastomoses) should be performed gently to minimize damage to the internal sphincter.
3. Transrectal dilation and irrigation.
Drug therapy is usually ineffective in patients with anastomotic stenosis and sclerotomy formation. We recommend that patients with low-grade rectal cancer start index finger dilation as early as possible about 1 week after surgery to reduce the probability of anastomotic stricture. The patient’s family is instructed to do this at home, once a week, in order to pass the index finger smoothly, with gentle movements, and without forcing the diameter to be enlarged. For patients who have developed a rigid canal, if the index finger is not passable, endoscopic anastomotic dilatation can be performed. A guide wire is left in place through the stenosis and a graded dilating balloon is placed along the wire, which is inflated step by step to dilate the anastomosis to about 2 cm. This operation carries some risk of anastomotic perforation, rupture or bleeding with serious adverse consequences and is therefore best performed in an experienced endoscopy center. In foreign countries, transanal retrograde colonic irrigation has been widely used for various intestinal disorders such as intractable constipation and fecal incontinence. In recent years, this technique has also begun to be applied in the treatment of ARS, and it has been reported in the literature that transanal irrigation can lead to improvement of symptoms such as fecal incontinence and voiding disorders in patients with ARS.
4. Practice active anal contraction.
Foreign scholars have reported that patients perform active anal contraction with the help of health care workers or family members. While contracting, the patient’s contraction action is evaluated by transrectal endoluminal ultrasound, manometry device or rectal palpation, and feedback is given to the patient so that he or she can perceive the changes produced by the contraction, intensify the training, and finally master the method of controlling the contraction of the anal sphincter, called biofeedback therapy. This technique can improve the quality of life of patients with rectal emptying disorders and reduce sphincter ataxia and the number of bowel movements, but it has not been widely adopted in China. We recommend that patients start to consciously and actively contract the sphincter in the early postoperative period, alternating between contracting anal action and fecal action for 30 min twice a day. on the one hand, it can prevent the formation of anastomotic sclerotomies, and on the other hand, improve the strength of the anal sphincter.
5. Other treatment methods.
Some scholars have reported that sacral nerve stimulation can improve the symptoms of ARS incontinence and improve the ability to defecate. The mechanism may be that it directly stimulates the anal sphincter to increase resting and fecal pressure, and also reduces prograde colonic peristalsis and increases retrograde peristalsis. For patients with severe incontinence or difficulty in fecal evacuation and intestinal obstruction, if the symptoms are still not relieved 1 year after surgery, a permanent colostomy should be performed to relieve patients’ hardship and improve their quality of life.
6. Rational selection of cases and adequate doctor-patient communication.
Since most of the existing treatments can only relieve symptoms, surgeons are often in an awkward situation once ARS occurs. For patients with postoperative anastomotic complications and great risk of ARS, APR instead becomes a better choice in order to ensure quality of life. Surgeons should not be obsessed with surgical techniques at the expense of protecting physiological function. Although new surgical techniques are emerging, including colonic-anal anastomosis, Parks procedure and Bacon’s procedure with ultra-low anastomosis, it is meaningless to preserve the anus if it only preserves the shape but not the function, and the patient’s quality of life is not high after surgery. Therefore, surgeons should be realistic in choosing anus-preserving surgery and strictly grasp the indications for anus preservation. For patients undergoing anus-preserving surgery for low to medium rectal cancer, especially for patients with low anastomosis or ultra-low anastomosis, adequate preoperative doctor-patient communication is essential. It is important to fully explain the possible complications of anastomotic fistula, bleeding and ARS with ultra-low anastomosis, and to obtain informed consent and understanding from patients.